Writing and testing async JS with Jest, promises and async functions

__tests__getStuff-test.js

jest.dontMock('../getStuff');

describe('getStuff', () => {
  let getStuff;
  let request;
  let stuffStore;

  it('loads the data', () => {
    const id = 1;
    const data = {a: 1};

    stuffStore = require('../stuffStore');

    request = require('request');
    // mock request() to return a promise resolving to a mocked response 
    // object, which has a method called .json(), which returns a promise 
    // resolving to the data object.
    request.mockImpl(() => {
      return Promise.resolve({
        json: () => Promise.resolve(data),
      });
    });

    getStuff = require('../getStuff');

    // kick off the request
    getStuff(id);

    // resolve all promises
    jest.runAllTimers();

    // make assertions about what should have occurred
    expect(stuffStore.startLoading).toBeCalledWith(id);
    expect(stuffStore.loaded).toBeCalledWith(id, data);
    expect(stuffStore.failedLoading).not.toBeCalled();
  });
})

getStuff-async.js

// async function based version
import request from 'request';

import stuffStore from './stuffStore';

export default async function getStuff(id) {
  stuffStore.startLoading(id);

  try {
    const res = await request('/stuff/'+id);
    const data = await res.json();

    stuffStore.loaded(id, data)
  } catch (err) {
    if (!err instanceof request.RequestError) throw err;
    stuffStore.failedLoading(id, err);
  }
}

getStuff-sync.js

// synchronous version which would block the browser while waiting for data
import request from 'request';

import stuffStore from './stuffStore';

export default function getStuff(id) {
  stuffStore.startLoading(id);

  try {
    const res = request('/stuff/'+id);
    const data = res.json();

    stuffStore.loaded(id, data)
  } catch (err) {
    if (!err instanceof request.RequestError) throw err;
    stuffStore.failedLoading(id, err);
  }
}

getStuff.js

// promise based version
import request from 'request';

import stuffStore from './stuffStore';

export default function getStuff(id) {
  stuffStore.startLoading(id);

  request('/stuff/'+id)
    .then(res => res.json())
    .then(data => {
      stuffStore.loaded(id, data)
    })
    .catch(err => {
      if (!err instanceof request.RequestError) return Promise.reject(err);
      stuffStore.failedLoading(id, err);
    });
}

stuffStore.js

const stuffStore = {
  startLoading(id) {
  },
  loaded(id, data) {
  },
  failedLoading(id, err) {
  },
}

export default stuffStore;